When more than two channels of a Wavelength-Division-Multiplexed (WDM) laser operate simultaneously in continuous-wave Is mode, wave-mixing (X.sup.(3)) in the passive shared waveguide can cause laser instabilities, resulting in spontaneous fluctuations in frequency and power. This problem is especially pronounced in WDM lasers that use a shared dispersive element, and in WDM systems where channel spacing is uniform.
Shared angular dispersive element lasers (SDELs) are a set of lasers that share the same intracavity angular dispersive element, such as a reflective or waveguide grating. Examples are the multiple-stripe array grating in a cavity (MAGIC) laser [1] and the waveguide grating router multifrequency laser (MFL) [2]. (Note, the number in brackets refers to a reference listed in the Appendix.) SDELs are well suited for WDM communications since they provide a large set of accurately spaced lasing wavelengths. MFLs have been demonstrated in systems experiments when operated continuous wave (cw) one channel at a time [3], and directly-modulated all channels at the same time [4]. It would also be useful to run all the lasers cw simultaneously, providing a source for long-haul WDM networks in which only one wavelength would have to be tuned to a reference, the rest of the lasers automatically aligned.
Wavelength-division-multiplexing (WDM) sources that consist of many lasers all sharing the same intracavity angular dispersive element (filter) are valuable because they can provide many wavelength channels simultaneously, the wavelengths inherently accurately spaced.
Undesireably however, in such a MFL source the laser signals may interact with each other via wave-mixing to produce unwelcomed crosstalk.